1. Field of the Invention
This invention relates to electromagnetic relays in which armature blocks are operated to pivotally move on insulation bases by electromagnetic force so that contacts are being switched over. In addition, this invention also relates to apparatuses and methods for manufacturing the electromagnetic relays.
This application is based on Patent Application No. Hei 11-120717 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Normally, electromagnetic relays that operate to switch over contacts are constructed by insulation bases and armature blocks, for example. Herein, the armature blocks are supported by the insulation bases in such a way that they are capable of moving in a pivotal manner under effects of electromagnetic fields. Specifically, the insulation base of the electromagnetic relay has a fixed-side terminal set including fixed contacts, a sectionally U-shaped iron core (hereinafter, simply referred to as a xe2x80x9cU-shape iron corexe2x80x9d having a cross section which is basically formed in rectangular shape, one side portion of which is opened), and a permanent magnet, all of which are integrally held by a fixed-side insulator. Herein, a coil is wound about a middle portion of the U-shape iron core, and the permanent magnet is inserted and engaged between side-end portions on both ends of the U-shape iron core. In addition, the armature block of the electromagnetic relay has moving-terminal members including moving contacts, and armatures which can be arranged opposite to each other at the side-end portions of the U-shape iron core, all of which are integrally held by a moving-side insulator. Thus, the armature block is supported in such a way that it is able to pivotally move towards the permanent magnet of the insulation base.
Conventionally, the electromagnetic relays of the aforementioned type are designed to have insulation bases, which are manufactured as follows:
A permanent magnet is inserted and engaged between side-end portions on both ends of the U-shape iron core in which a coil is wound about a middle portion. The side-end portions and permanent magnet are fixed together in advance by welding or bonding which is effected using adhesive, so that a joint unit is being made. Such a joint unit is arranged in a metal mold together with the fixed-side terminal set. By the metal mold, the fixed-side terminal set is integrally formed with the joint unit of the U-shape iron core and permanent magnet.
The aforementioned manufacturing technique is disclosed by Japanese Unexamined Patent Publication No. Hei 6-196063, for example.
Since the conventional electromagnetic relays are manufactured such that the permanent magnets are fixedly attached to the side-end portions of the U-shape iron cores by welding or bonding using the adhesive, they suffer from problems, as follows:
(1) When the permanent magnet is fixedly adhered between the side-end portions of the U-shape iron core by welding, sputters in welding are frequently adhered to contact surface portions between the armatures and side-end portions of the U-shape iron core. This causes defectiveness in contacts between the side-end portions and armatures. As a result, magnetic resistance between the U-shape iron core and armatures is remarkably increased. This brings reduction in yield of products being manufactured.
(2) At integral molding of the joint unit which is made by welding by which the permanent magnet is fixedly adhered between the side-end portions of the U-shape iron core, molding burrs are produced from weld portions due to dispersion in amounts of melted matters in welding. When the molding burrs reach the contact surface portions between the armatures and side-end portions of the U-shape iron core, reduction occurs in yield of products being manufactured.
(3) When the permanent magnet is fixedly adhered between the side-end portions of the U-shape iron core by bonding using the adhesive, it is necessary to provide a wait time for waiting for hardening of the adhesive. This brings reduction in productivity of joint units each of which has a U-shape iron core and a permanent magnet being adhered to each other.
(4) The conventional technique requires two steps, i.e., a first step for manufacturing a joint unit having a U-shape iron core and a permanent magnet, and a second step for fixing the joint unit and fixed-side terminal set to the fixed-side insulator by its integral molding. So, it cannot be said that productivity is sufficiently high.
(5) The conventional technique firstly joints a U-shape iron core and a permanent magnet together to form a joint unit. Thereafter, the joint unit and fixed-side terminal set are fixed to the fixed-side insulator by its integral molding. Hence, first error is caused to occur at joint of the U-shape iron core and permanent magnet, and second error is caused to occur at integral molding of the fixed-side insulator. Those errors are accumulated to badly influence positional accuracy in fixing the fixed-side terminal set and the U-shape iron core or permanent magnet in prescribed positions. That is, if positioning of the joint unit is made based on a fixed position of the U-shape iron core in the metal mold, a positional accuracy is deteriorated with respect to the fixed-side terminal set against the permanent magnet. If positioning of the joint unit is made based on the fixed position of the permanent magnet in the metal mold, a positional accuracy is deteriorated with respect to the fixed-side terminal set against the U-shape iron core. In both cases, reductions are caused to occur in electric characteristics of the electromagnetic relays being manufactured.
It is an object of the invention to provide improvements in a mechanical construction of an electromagnetic relay in which magnetic resistance between a U-shape iron core and armatures is reduced and in which positional accuracy in positioning of fixed-side terminal set with a U-shape iron core and a permanent magnet is improved.
It is another object of the invention to provide an apparatus and method for manufacturing electromagnetic relays with a good yield and good productivity, in which manufacturing steps are simplified by eliminating an unwanted wait time for waiting for hardening of adhesive used for bonding effected between side-end portions of the U-shape iron core and permanent magnet.
An electromagnetic relay of this invention is basically constructed by an insulation base and an armature block. Herein, the insulation base is constructed by a fixed-side terminal set including fixed contacts, a coil block in which a coil is wound about a middle portion of a U-shape iron core, and a permanent magnet, all of which are integrally held together by a fixed-side insulator. The armature block is constructed by a moving-side terminal set including moving contacts, and an armature, all of which are integrally held by a moving-side insulator. The armature block is mounted on the insulation base in such a way that the moving contacts are placed opposite to the fixed contacts respectively, and the armature block is supported by a support point to pivotally move on the permanent magnet under an effect of electromagnetic force. Specifically, the fixed-side insulator is made by molding using resin material to integrally hold the fixed-side terminal set, coil block and permanent magnet together at prescribed positions, so it is possible to improve an accuracy in positioning of the aformentioned parts of the insulation base. In addition, the fixed-side insulator is formed in a prescribed shape having a contact fixing portion that partly extends to provide engagement portions by which the permanent magnet and U-shape iron core are tightly fixed together under a contact condition where the permanent magnet is placed in tight contact with the side-end portions of the U-shape iron core. That is, the contact condition is established by pressing exterior walls of the side-end portions of the U-shape iron core to be in tight contact with terminal surfaces of the permanent magnet, then, integral molding is effected to integrally form the fixed-side insulator having the contact fixing portion whose engagement portions firmly attach the permanent magnet between the side-end portions substantially without forming spaces therebetween. Therefore, it is unnecessary to perform welding on the permanent magnet and U-shape iron core, so it is possible to prevent the side-end portions from being partially melted out due to sputters of welding. This brings good contact with respect to the armature, and it is possible to reduce magnetic resistance between the U-shape iron core and armature. In addition, it is unnecessary to perform adhesion using adhesive between them, so it is possible to simplify manufacture of the electromagnetic relay by eliminating a wait time for waiting for hardening of the adhesive. Thus, it is possible to improve yield and productivity in manufacturing electromagnetic relays.
Incidentally, positioning of the permanent magnet and U-shape iron core is actualized in a variety of ways in a metal mold. For example, the engagement portions are formed in hook shapes that engage with channels formed on an upper surface of the permanent magnet to face with the armature block. Or, they are formed in cylindrical shapes that engage with positioning holes formed to penetrate through the permanent magnet. Or, they are formed in elongated block shapes that engage with cut sections being formed on elongated sides of the permanent magnet. Or, they are formed in shapes that interconnect with positioning projections formed on the upper surface of the permanent magnet.
In addition, the metal mold is constructed using an upper mold and side molds. The side molds are moved to approach each other in a clamping mode to press the exterior walls of the side-end portions of the U-shape iron core to be in tight constant with terminal surfaces of the permanent magnet. In addition, an engagement channel is formed in the upper mold to engage with the permanent magnet and is formed to cope with a variety of shapes of the permanent magnet. For example, mold projections are formed in the engagement channel of the upper mold to partially engage with the channels of the permanent magnet.